1. Technical Field
This invention is a machine for feeding sheets of paper, and more particularly is a machine for feeding single sheets of paper from the bottom of a generally upright stack of sheets.
2. Background Art
A bottom sheet feeder is used to release a sheet from the bottom of a stack of sheets and to feed a released sheet toward form handling or form processing equipment. The cycle of releasing and feeding sheets is repeated continuously so that newly exposed bottom sheets are consecutively released from the stack and fed seriatim toward a processing line.
Friction-type bottom sheet feeders have a powered roller upon which a stack of sheets is placed. The weight of the stack bears against the roller to produce a friction force between the bottom sheet and the roller. When the roller is rotated the roller frictionally grasps the bottom sheet and releases the sheet from the stack. As the roller continues to rotate the bottom sheet is drawn from the stack and is advanced toward additional sheet feeding components. An adjacent sheet is exposed to the roller and the cycle continues until the supply of sheets in the stack is depleted.
The problem with present friction-type bottom sheet feeders is that the weight of a stack of sheets produces friction not only between the bottom sheet and the underlying roller, but also between each pair of adjacent sheets in the stack (with a relatively large friction force acting between adjacent sheets near the bottom of the stack because of the weight thereof). When the weight of the stack is large, for instance, when the number of sheets in the stack exceeds about 250 sheets, or when the sheets have interior perforations to facilitate subsequent tearing, the bottom sheet becomes frictionally engaged with one or more overlying sheets and the roller frequently feeds two or more sheets from the stack (referred to in the industry as "doubling") toward the processing line. Doubling causes jamming of equipment and necessitates costly shutdowns to clear a jam and resume processing. Doubling also reduces the smooth flow of sheets toward a processing line and limits the rate at which sheets are fed. Alternatively, the machine may not feed at all, known in the industry as "stalling".
One solution to the problem of doubling or stalling is to limit the size of the stack of sheets positioned on the roller. By using a smaller stack the weight of the stack and thus the magnitude of the friction force between adjacent plies is reduced and the likelihood of doubling or stalling is reduced. Machines which are limited to using a relatively short stack require constant monitoring and reloading to maintain a high feed rate, such as several thousand sheets per hour. Consequently, prior sheet feeders require extensive operator intervention merely to avoid the feeding of double sheets, thereby incurring additional time and labor cost in the sheet handling process.
The present invention is directed toward overcoming one or more of the above problems.